1. Field of the Invention
The present invention relates to a method for bonding copper foils to a ceramic substrate and more particularly, to an advanced copper bonding (ACB) with ceramic substrate technology for making a composite plate by: depositing a copper film on a ceramic substrate by a sputtering technique, and then electroplating a copper layer on the copper film to form a composite copper layer at the ceramic substrate, and then pressing a copper foil on the composite copper layer with ceramic substrate by putting the copper foil on the composite copper layer with ceramic substrate in a high-temperature sintering furnace to let the composite copper layer and the copper foil be bonded into a copper strip by a diffusion bonding technique under environments of high temperature, vacuum, and negative pressure caused by inert gas or H2 partial pressure.
2. Description of the Related Art
The currently popularly used method for bonding copper foils to a ceramic substrate is DBC (direct bonding copper) technology. This technology includes the process of forming copper oxide at the interface of each of two copper foils, the step of attaching the copper oxide-coated copper foils to a ceramic substrate, and the step of employing eutectic sintering under temperature 1065˜1083° C. to have the copper oxide-coated copper foils and the ceramic substrate be bonded together.
U.S. Pat. No. 5,490,628 discloses a technique of directly bonding a ceramic member to a copper composite substrate by heating to diffuse copper to the surface of the copper composite substrate at 1200° C., oxidizing the surface of the copper composite substrate following heating, pressing a ceramic member in contact with the resulting oxidized substrate, and forming a copper-copper oxide eutectic at the interface between the copper composite substrate and the ceramic member by heating under temperature 1065˜1083° C. The eutectic, upon cooling, forms a bond between the copper composite and the ceramic.
U.S. Pat. No. 3,766,634 discloses a method for direct bonding of metallic members to non-metallic members at elevated temperatures in a controlled reactive atmosphere by: pressing copper in contact with alumina substrate, heating copper and alumina substrate in a reactive atmosphere to create a copper-copper oxide eutectic melt which, upon cooling, bonds the copper to the substrate.
U.S. Pat. No. 4,505,418 discloses a method for directly bonding copper foils having a copper oxide layer to oxide-ceramic substrates by heating the ceramic substrate covered with the copper foil in an oxygen-containing atmosphere at a pressure of not more than 1 mbar while maintaining a furnace atmosphere with a partial oxygen pressure between 0.001 and 0.1 mbar.
Taiwan Patent Application 096148408 discloses a method for preparing a composite plate by: preparing a ceramic substrate and a copper foil; forming a layer of copper oxide at one surface of the copper foil by wet air oxidation; bonding the layer of copper oxide of the copper foil to one surface of the ceramic substrate by heating.
According to the aforesaid various prior art techniques, bonding a copper foil to a ceramic substrate is done by: forming a layer of copper oxide at one surface of the copper foil and then pressing the copper foil and the ceramic substrate in a sintering furnace for heating at a temperature above the eutectic melting point and below the melting point of copper. These prior art techniques require a complicated manufacturing process. If an aluminum nitride ceramic substrate is used, it is necessary to form a layer of aluminum oxide on the surface of the aluminum nitride ceramic substrate for bonding with the layer of copper oxide at one surface of the prepared copper foil by eutectic sintering. This technique involves multiple heat-treatment processes, wasting much energy.